THE DIGESTIVE TRACT OF ELASMOBRANCHS. Us 
of putrefaction. Furthermore, this investigator saw that the acid is secreted by the 
stomach and that it might be seen exuding from the walls. He did not make men- 
tion, however, of digestion in the intestines or of the action of the bile. In his eyes, 
indeed, the stomach in all animals was the principal digestive organ. 
Tiedemann and Gmelin (1827) made observations upon the contents of the intes- 
tinal tract of the trout ybarbel (Cyprinus barbus), etc., and proved that in a fasting fish 
the mucus does not redden litmus, but that a stomach full of food contains free acid 
and coagulates milk. Tiedemann and Gmelin believed that the acidity is due to a 
mixture of acetic and hydrochloric acids. These workers also paid some attention to 
the liquid of the pyloric appendages. This liquid, they found, reddens litmus but 
slightly, and they believed that it mixes with the food dissolved by the stomach and 
accelerates assimilation. 
In 1873 Fick and Murisier called attention to the fact that the ferment in the 
stomach of the trout and the pike differs from that of higher animals in that it 
digests food at a low temperature as well as at 40° C., while the higher organisms 
digest better at the higher temperature. 
In the same year Rabuteau and Papillon (1873) recognized that the gastric juice 
of the skate is acid, and the former writer secured, by distillation, a colorless liquid 
which he considered hydrochloric acid. 
A little later Homburger (1877) concluded from his researches upon Cyprinus 
tinca, Chrondrostoma nasus, Scardmius erythrophthalmus, and Abramis brama that 
the bile and extracts of the liver of these animals, as well as extracts of the intestinal 
mucous membrane, digest fibrin, emulsify fats, and convert starch to sugar. 
In 1877 Krukenberg carried on investigations upon the intestines, and then upon 
the glands connected therewith, of widely different species belonging to all classes of 
fishes except dipnoans. From this work he concluded as follows: 
No fish possesses salivary glands, although some have a diastase in the mucous membrane of the 
mouth, as, for example, Cyprinus carpio and Lophius piscatorius. 
The action of the stomach is variable. With some selachians, ganoids, and teleosts this organ 
secretes pepsin similar to that of mammals in that it acts only in an acid medium, but different in that 
it can act at a lower temperature. In some cases, as in certain teleosts (Zeus faber, Scomber scomber), 
the stomach produces pepsin only in its anterior part, while the fundus secretes a mixture of pepsin 
and trypsin or a juice capable of digesting fibrin in an acid or in an alkaline medium. With other 
teleosts (Gobius, Cyprinus) the stomach, or the organ, considered as such does not furnish any enzyme 
at all. Digestion in these instances is carried on exclusively in the middle intestines. 
In the selachians and the ganoids pepsin is produced not only in the stomach, but also in the 
anterior end of the middle intestines, in the selachians to the place where the pancreatic duct empties, 
and in the ganoids to the pyloric appendages. 
In the selachians the massive pancreas secretes trypsin, while in the ganoids and teleosts, which 
have a diffused pancreas mixed with hepatic tissue, a ferment similar to pepsin can be extracted from 
the liver. This ferment is absent from the liver of the selachians. 
In the case of the Cyprinidze trypsin is found both in the liver and in the mucous membrane of 
the middle intestine. The middle intestine, indeed, should be regarded as the principal seat of 
digestion in these fishes. 
As regards the function of the pyloric appendages in most fishes, they inclose only mucus and 
chyle and are absorbing organs, while in other cases they secrete either a trypsin-like ferment, as in 
the Thymnus vulgaris, a mixture of pepsin and trypsin, or sometimes a mixture of pepsin, trypsin, and 
diastase. 
Finally, in many species the liver, or hepato-pancreas, and the middle intestine secrete a diastatic 
ferment, as does even the buccal mucous membrane. 
